Acute Myocardial Infarction (AMI, also referred to as heart attack) remains a leading cause of mortality in the developed world. Finding accurate and cost-effective solutions for AMI diagnosis is vital. Survival of patients having AMI may depend critically on reducing treatment delay, and particularly reducing the time between symptoms onset and medical treatment time. A technology that would enable AMI diagnosis early after occurrence of AMI symptoms, for example, at patient's home or where ever the patient may be, may significantly decrease AMI mortality.
In the AMI setting, the conventional 12-lead ECG is not only the most important piece of information, but it is also nearly as important as all other information combined. Therefore, a technology for early AMI diagnosis may rely on ECG recording. The ECG recording may be performed by the patient himself, but such a technology would need to overcome the problem of complicated application of 12-lead ECG electrodes, and to enable automated software based AMI detection.
Electrocardiogram (ECG) data recording as acquisition of bioelectric signals for cardiac condition status detection is widely known in the art. In general, before the recording is performed, characteristic points on patient's body are identified and electrodes are positioned with respect to these points. During the recording procedure, the electrical voltages between two characteristics points are measured, and corresponding signals are called ECG leads. The conventional ECG uses 10 electrodes to record 12 leads, and the 12 leads ECG (12L ECG) is widely adopted standard in cardiac diagnostics.
It has long been suggested that urgent cardiac diagnostics which enables a patient, wherever he may be, to record his ECG himself and send it to his cardiologist in the remote diagnostic center via commercial telecommunication network (cellular or similar) would be beneficial. On the bases of the received ECG and the conversation with the patient, the cardiologist on duty could decide whether the patient's state requires urgent medical intervention, and act accordingly. There are a number of patents and products which, within the said concept of urgent cardiac diagnostics, offer different solutions for recording and transmitting the ECG signal. The simplest of these devices uses only a single ‘lead’ or pair of electrodes. However, devices recording only one ECG lead may be used only for rhythm disorders. Because the ECG changes needed for detection of an AMI may occur in as few as only two among 12 leads of a conventional ECG, it may be difficult, to reliably use only a single lead (or in some cases only a few leads) to reliably and thoroughly detect AMI. Further, it is also unreasonable for a patient to record a full 12L ECG by himself, because of the difficulty in placing the leads.
Solutions capable of detecting AMI that use different surrogates of 12L ECG are also known. For example, Heartview P12 by Aerotel (Aerotel Medical Systems, Holon, Israel), Smartheart, by SHL (SHL Telemedicine, Tel Aviv, Israel) and CardioBip (e.g., U.S. Pat. No. 7,647,093). All these solutions have significant drawbacks. For example, all of these solutions typically require complicated measuring procedures (such as with Heartview, Smartheart), and may require attaching electrodes by the means of cables, taking the clothes off from the waist up, using straps and multi-step recording procedure (e.g., see US20120059271A1 to Amitai et al.). Existing or proposed systems may also require extensive calibration procedures (e.g., Cardiobip), requiring the patient to be in a medical facility with specially trained personnel prior to using the device by himself. Finally, all of these procedures may require medical personnel for interpretation of recorded ECG.
For example, the Cardiobip device is the simplest for use by the patient, and allows simple positioning of the device by pressing it against the chest, with no cables or straps, and recording the ECG. In this example, a diagnostic center may use a PC computer with corresponding software for processing of three special ECG leads and reconstruction of the three leads into a standard 12 lead ECG. The reconstruction is required for interpretation of ECG by the medical personnel. Accuracy of the reconstruction of a 12 standard ECG leads using the recordings of three special leads may be achieved by strictly determined arrangement of integrated electrodes in the mobile device and corresponding leads. A hand-held device may include 5 built in electrodes (see, e.g., EP1659936) three of which may be placed in contact with the chest of the patient and the remaining two electrodes in contact with right and left hand fingers. The reconstruction algorithm in the Cardiobip device is premised on the assumption that the diffuse electric activity of the heart muscle can be approximated by a time-changing electrical dipole (heart dipole) immersed in a low conducting environment. The Heart dipole is represented by a vector defined by three non-coplanar projections, so that it can be determined on the basis of recording of electric potential between any three pairs of points corresponding to three non-coplanar directions, i.e., three special ECG leads not lying on the same plane. Standard ECG leads are reconstructed as linear combinations of the recorded special leads and coefficients by which the transformation matrix is defined. It can be shown, by an in depth analysis, that there are two dominant error sources in such reconstruction. Unfortunately, the heart dipole is only the first term in the multipole mathematical expansion of diffuse heart electrical activity and this approximation is valid only for recording points at a sufficient distance from the heart. In the points near the heart, the linearity of the system necessary for signal reconstruction is significantly affected by the non-dipole content created due to the presence of higher order terms in multipole expansion.
Further the described reconstruction techniques for converting a few leads into a 12 lead signal for analysis by a cardiologist or other technical expert are also limited. In order to carry enough diagnostic information the three special leads need to be as close to orthogonal as possible (e.g., three vector axis with 90 degrees angle between each of them). The opposite to orthogonal is the case of three coplanar vectors, that is three vectors in the same plane, in which case the diagnostic information corresponding to the axis perpendicular to that plane is completely missing. Importantly the assumptions needed for this modeling, treating the heart as a dipole (and estimating at a distance) and making orthogonal measurements of the heart leads, are at odds with each other, since the orthogonal lead positions are far easier to obtain if the electrodes are closer to the heart, while in this case the non-dipole content is higher. Existing systems such as Cardiobip must rely on the use of a configuration that optimally fulfills both requirements, in which all three leads use the right hand electrode as a reference. These systems also have additional drawbacks. For example, Cardiobip uses three integrated electrodes on the chest side of the device. It was observed in clinical studies using Cardiobip that breast in female patients and pronounced pectoralis muscle in male patients may prevent a reliable contact of all three electrodes with the chest surface simultaneously. It has also been observed that the symmetrical arrangement of finger electrodes on the front side of the device may cause switching of left and right hand fingers in about 10% recordings, making the recording useless for diagnostics.
Similarly, other solutions that use a reduced set of three leads (e.g., US20140163349A1; US20100076331) typically use the three leads that are coplanar and therefore lack enough diagnostic information for AMI detection.
In addition, the requirement for trained medical personnel for the interpretation of recorded ECG may be an organizational challenge and increases the operational cost of the system, and the accuracy of the human ECG interpretation may have large variance. Automated software for ECG interpretation is also used in the systems for early diagnosis of AMI, but they have performance that is inferior to that of human interpreters. The chest pain is the main symptom suggesting an AMI, or ischemia (the underlying physiological process). The main ECG parameter used is the ST segment elevation (STE). Unfortunately, a large number of patients (up to 15%) presenting with chest pain have STE of non-ischemic etiology (NISTE) on their presenting (to the emergency room) ECG. Thus, both human readers and automated software may often misinterpret NISTE as a new STE due to ischemia. In a typical emergency room (ER) scenario, patients with chest pain are examined by emergency physician who must promptly decide if the acute ischemia is present, relaying just on the on-site (current) ECG recording.
Thus, it would be advantageous to provide a technology capable of separating new from old STE, as it could significantly increase performance of automated AMI detection, and make it a viable enhancement or even replacement for human interpretation, particularly when qualified human interpretation is not available. Described herein are methods and apparatuses that may address the problems and needs discussed above, particularly the need for early automated remote diagnostics of AMI. In particular the methods and apparatuses described herein may provide a mechanically stable and improved electrical contact, while eliminating errors associated with switching of finger contacts.